That Day
by xxredemption-love-and-liesxx
Summary: "kid, why were you there? why did you climb the mountain?" / In which Sans eventually asks a question which has been bothering him a long time.


**That Day**

 **Summary:** "kid, why were you there? why did you climb the mountain?"  
 **Warning:** Dark topic ahead.

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 **I** t had always bothered him. Well, ever since he got to _know_ the kid and genuinely understood that they were a kind person (even with the mishaps with other timelines and them _committing genocide_ ), and did not deserve anything ill-thought towards her. The kid was just someone he had genuinely come to care about; worry after. She meant the world to so many monsters (especially Toriel), and she meant the world to him—after all, his soul literally _called_ for her( **1** ).

Kids should not be climbing mountains.

He had seen it in the others that had made their way through the Underground. They each had their own reasons for climbing the damn thing in the first place. Whether it be to escape from reality or simply to explore the unknown, the reasons were… varying. Some of the children were notably more so up there for more _sinister_ reasons, finding no reason to live.

However, _his_ kid never said anything about it—never uttered a word about it. She just acted aloof when anyone nudged onto the topic, and she acted like she knew nothing. It really was aggravating to watch, especially for someone who could usually figure out someone's intentions without them even _saying it_.

In her case? He was simply not sure.

She could have been up there for exploration—and to him, that made _more_ sense. If she wanted to die, would she not have taken her life the moment she found that _toy knife_? Sure, it was a toy, but the damn thing did have an _edge_ to it. He had seen it glint in her hands multiple times before, so he should know.

If she wanted to die, she could have tossed herself into the boiling lava in Hotland or tied herself to some rocks and drown in Waterfall. She could have wandered around in the cold in Snowdin, or allowed monsters to _kill her_ in the Ruins. She had many chances to die. So many chances. That was why he was not _sure_ whether or not it was what she intended, then again, maybe it was to escape—to escape from her own home.

Toriel had asked them the moment everyone escaped whether or not the kid wanted to stay with her, or to go elsewhere—Sans assumed Toriel was meaning the kid's own family.

The kid stayed with Toriel.

Didn't humans have strong connections with family members like he did his own brother? Or were they more detached in that area, like they are with their mates?

She should have had a home to return to, especially a kid as kind as that.

Still, Sans was not the sort to pry, so he would not ask her directly about it. He could easily look it up—he knew what her _old_ last name was, according to letters she had received from… _someone_ —he could not help but feel instinctual possessiveness at that—though, she burned them as soon as she received them, so he did not have the ability to _look at them_ and find out who this person was.

Did Frisk really want to avoid _whatever it was_ that much?

.

It was a usual day in Aboveground. Sadly, Asgore was the one who named the town that had been created for monsters. Asgore had named everything else—Ruins, Waterfall, the Capital. Aboveground was a small town located off of a busy highway. It got lots of people who came through simply because this was where _most monsters_ lived—though, others decided to live elsewhere on the planet.

Monsters made sure to keep in touch with each-other, but _some_ monsters wanted to start anew in a world filled with humans. It was weird, but Sans could see where they were coming from. Some people wanted to be able to incorporate themselves in other places so monsters were not _just_ found in one area. It could potentially cause racism in the future, and he guessed that some monsters had been asked by the King.

… Not that Asgore was much of a king anymore. It seemed that Tori had taken over that right—well, as being a queen. She seemed to better understand humans, and had more control over others due to her kindness. Asgore seemed to bow down to whoever intimidated him, while Toriel combated against any and all threats.

She was a fit ruler, Sans knew.

He and his brother stayed in Aboveground, though Papyrus made it pretty clear he wanted to travel at some stage. Sans would allow them both to do that when they could hold down funds easier. Money was still scarce—no longer was it gold but paper notes and virtual funds. Though, gold was exchanged for _said money_ and many monsters were lucky.

Muffet being one of the lucky ones. She started a small company of restaurants which spanned across the entire country of the United States. Sans knew that she was getting more and more popular each and every day, and she was able to expand whenever she wanted, really.

Seven years on the surface would probably do that to anyone.

There had been a few issues integrating into human society. Some humans believed that _all_ monsters were evil due to them having been shoved into the Underground many years ago. Apparently, any and all records had been tarnished due to fear in the populace of monsters remerging and wanting revenge. The government did not want to have that risk, especially with the grave sin they had committed in the first place.

Hilariously, they were a few monsters which were spared from being sent to the Underground, but they were often captured and used for experimentation.

Toriel was able to use that as an 'eye for an eye' when it came to the deaths of the seven humans.

Monsters had become a myth to many humans, and many humans had been shocked with their return. _Some_ older humans remembered monsters, but due to pay offs, they were unable to speak of them.

Children were either terrified or completely at ease with monsters, though many of them were now happy with their presence in society.

Adults were less… welcoming. They believed that monsters would eat them and their children, and that they would take over—it took a lot of talks between the government and Toriel (with the help of Frisk) to stop this. Though, as with anything, humans were still worried.

All of the monsters ended up with occupations. Undyne was listed as a reserve for the army, but was a personal trainer for many humans and monsters; Alphys became a biologist within the government's ranks; Asgore became a politician of sorts (and part time gardener); when Tori was not involved in her duties as queen, she was found in the kitchen of a very fancy restaurant; Papyrus was also a chef—having learned how to cook _much better_ ; and Sans was a physicist that did his own works (but got paid for any contributions he gives). Really, everyone had learned how to _be_ in society.

 _Except_ for Mettaton who took the world by storm as an actor alongside his cousins Nabstablook and Angry Dummy (although, Nabstablook was more well-known for his dubstep and chillstep).

.

His question about Frisk was one that Toriel had asked him multiple times; for whatever reason, she believed that he would know about it seeing as Frisk was extremely open when it came to him (not that Sans could disagree, but…).

Sans was not one to press on about a topic which was easily viewed as being sensitive, but he felt that he could not sit idly by with this. Whatever had happened to the human child was worrying himself and her adoptive mother, and it was something that could potentially cause issues in the future—Sans and _Toriel_ really needed to know about it, in case something came up.

So, when he asked her openly about it, she instantly closed off, clutching onto her leg and looking away—she was just _fifteen_ for God's sake… She was _eight_ in the Underground, and if his suspicions were correct, then maybe she needed some help… even if it did not seem it.

After all, he was someone who was diagnosed with depression and hides behind his alcohol, grin and humour.

You never really know how someone is going unless they let you in, and Sans hoped that she trusted him enough.

"c'mon kid, no one climbs that mountain for no reason," Sans said, patting her on the pack, and pulled his hand away lightning fast when she openly flinched at this.

He stared at her, his usual grin falling away as fear hammered in his chest. M… Maybe he should have kept quiet about it, like he was planning to? It was not his business, after all… she did not have to answer him, and she _sure as hell_ did not have to tell him about a damn thing.

He could see that she was uncomfortable, allowing her brown bangs to cover her equally brown eyes.

"kid… sorry, it's just. it's just been there for a while, you know. i just don't get it, and i wanna get it, so like…" he scratched the back of his skull, causing a rattling sound as he tried to _magically_ gauge her reaction, "… look, you don't have to answer me or nothing. i mean we all got… _skeletons_ in the closet, but…"

She let out a dry laugh, brushing her hair away as she stared up at him with an uneasy grin, "No, it's okay. It just… took me by surprise…"

Silence enveloped the two as the human clutched down on her clothing, avoiding his penetrating gaze. He was trying to understand—to read her. He was good at reading anyone, plus, he could summon her soul to see what she was seeing, anyways. Even a _determined_ kid would not be able to hide their emotions for long. He could just _check_ her, and he would know his answer.

However, that was wrong—even for someone as messed up as him.

"I… was wondering when one of you were going to ask about it. Mother seemed worried about it, and… I don't know. People try to bring it up, but I'm just… not sure whether or not I should answer. Everyone had their own problems— _has_ —their own problems. Mine aren't… They're just…"

Sans swallowed the lump in his throat… well, the non-existent one that he had just conjured in his hesitation. He opened his jaws before closing them again, looking down from her. The way she was hesitating… he was sure that there was something sinister to it, like he had expected…

"You know, before I fell into the Underground…" she whispered, staring up at the ceiling before she made her way to the closest couch and sat down, before patting her hand, and asking for Sans to sit beside her—the skeleton obliged easily, "… I didn't have parents. I didn't know anything about what it was like. My mum—my biological one—apparently dropped me on a doorstep before running away into the night. The woman there just gave me over to the orphanage, unable to look after me. The orphanage was, well, near the mountain. Something about the mountain always _got me_ , but you see, we weren't allowed out. The nuns did not like us wandering, and they had such strict rules for us—the mountain being a big _no-no_ to them."

Sans was surprised the kid was even telling him about this… she was just…

She dropped her head, playing with her fingers in a nervous manner, "I never was adopted. I got older and older, and people said that the older I got, the less likely I would be to get adopted. I guess… I guess I just…" she blinked, rubbing her eyes and Sans wanted nothing more than to hold her, as he felt his own soul quiver with guilt and sorrow, "… I got low. I found… a razor. I kept it under my pillow. I just… I just wanted to escape for a bit. The other kids were so… so _mean_ , you know. They would tell me that I would never get adopted. One by one, these kids got adopted… and I guess... one day I decided that…"

The skeleton pulled her close, holding her into him as she let out a whispery sob. It was so low, that he was sure if he were a human that he would not have heard it.

Yet, he was a monster and could _definitely_ hear it.

It pained him—he just…

How could she…?

"… I ended up cutting, maybe three times a week. My wrists, my legs, my chest… anywhere that I could kind of hide," Frisk let out a sob, clinging onto the skeleton next to her, "The nuns noticed one day… they brought me out into the yard and they just…"

She shook her head, "That night… I decided to leave. I just… climbed out an open window and made my way onto the mountain. Then… after a while of walking, I woke up in the Underground."

Sans released a shaky breath—why would she…? How _could they_? He wanted to _tear them a part_. His magic flared in his right socket as he clutched onto her arm, the light of his eye illuminating the room in a gentle blue glow.

"I wanted to die, Sans…" Frisk muttered, her voice so low and _different_ that Sans was surprised it was still her, "… but yet, I woke up here. I didn't get it… I accepted death when Flowey wanted to kill me, but I was saved… then I met Toriel, and later… you… and Pap… everyone…" she smiled through her tears, looking him in his glowing eyes, "You guys helped me—allowed me to find the _determination_ to live on, even when I thought everything was lost. I found a mother and I found friends…"

Sans allowed his anger to die, and so too did his magic. He pulled her onto his lap and hugged into her, not caring about anything else but the determined girl in his arms.

"What about _you_ , Sans?" she whispered after a moment, causing Sans to still as he pulled her back so he could stare at her, "' _Give up, I did_ '… what happened…?"

The smaller skeleton let out a 'heh', before holding onto her wrist, "welp… since you told me, i guess… it's my turn then…" he breathed, leaning in again, and resting his bony hands against her back, gently rubbing her spine through her shirt, "y'know at least i'm a scientist, right? i did give you the password in this timeline, but… i'm guessing i gave it to you before?"

Frisk nodded.

"well, before i became a scientist… i lived with my father and my brother… though, the old man was not around much, so i basically raised pap myself. dad only was around when he… needed subjects," Sans voice became gravelly at the end of that particular sentence, he pulled back, allowing his once again blue pupil to focus on her, "this power was thanks to him. paps… has it too. though, his experiments were more severe for me. i couldn't protect pap from dad… so…"

The human looked shocked and she was shaking slightly; he could feel it.

"… heh. i felt like shit for that. i remember… becoming a scientist when i was older. dad wanted me to take over his work, so i did. one day, some shit happened and he was clinging onto an edge that was hanging over what you probably know as the void," Sans' sockets narrowed slightly as he let out a heavy breath which he had been holding for a while, "i did somethin' pretty bad that day. i pushed him down, probably had a big grin on my face when i did it. the old man wasn't… happy. though, after that, i was the only one who remembered him. pap didn't remember his powers, and no one remembered him. except for me.

"i became the royal scientist for a while, y'see, gaster—dad—was the royal scientist before me. then alphys showed up and i practically walked out. pap and i moved from the capital and ended up in snowdin. we had _just_ enough money to buy a house there, and… welp. i didn't want pap to be workin', you know, so picked up three jobs—those sentry stations. undyne, alphys and the king didn't care because they knew i had my 'shortcuts'.

"well, things were ok for a while. then… you came along."

Frisk stilled, her eyes widening once more as she continued staring at him, she opened her mouth to say something, but Sans beat her to it.

"not sayin' you didn't bring any _good_ to my life, but you kind of complicated things. look, i already dealt with resets thanks to the _house plant_ but you… you i couldn't keep track of. i _kind of_ remembered timelines in dreams, and for a while i thought they were just that… then i started to sleep more and more… then realized that the world would be _reset_. for a while, my actions were pointless. i'd killed you a couple of time _prematurely_ , right? yeah. then you'd _reset_ and nothing changed. you just continued doing the same shit, so i gave up on that—plus, i'd broken tori's promise more than once… couldn't do that anymore.

"you were kind to begin with, then sometimes cruel, then cold. you made it to the end with me—you'd killed everyone, and i… i didn't even know why i was fighting at that point, you know. i just fought though, it seemed like _they_ wanted a challenge, and i gave them that. and i know i died and all that sorta shit, but whatever. and then you decided to not harm anyone in the next run… so i let you do whatever you pleased.

"but i knew you could turn that off with a click of your fingers. i'd repeated shit over and over, and basically—yeah, i didn't see a point. i knew i was getting depressed, but what did it matter? as long as i kept my brother safe, it was fine—but you and i _both_ know i couldn't even do that."

The human girl was absorbing the information she was being given, and she did not bother saying anything—to him, it seemed she was waiting until he would finish.

"you know, i'd killed myself a few times. though, i _know_ you know that, because after that, you'd always _reset_ … i dunno. it was weird. the anomaly wanted to help this time rather than kill, so… i guess i was curious to see how it ended. and i did… so i'm glad we're here now, is what i'm trying to say, i guess."

Silence once again fell between the two, before Frisk hopped off of Sans lap and rested her hands against her knees. She bit her lower lip as he stared at her, waiting for her reaction. He really had laid it all on the table. Even Papyrus did not know about the mysterious death of their father, and now he has to trust this kid to not say anything.

To be quite frank, he did not trust people all that well (almost as much as his disdain of making promises).

He did not want her to let anyone know about any of this, as it would just complications for them. Sure, he cannot say he _regrets_ killing his old man, but he could not phantom how his brother would react towards this. He did not want to have to deal with the look of betrayal on his face.

Besides, no one remembered W.D. Gaster anyways—his _fall_ into the void secured that. Sans only remembered because, well, it was a gnawing thing on his mind, even if the old skeletal monster slipped from his mind once or twice.

"I'm glad too, not… for _everything_ , obviously, but…" Frisk swallowed audibly as she reached for his bony phalanges and wrapped her fingers around his own, curling them slightly as they held hands, "… I guess things turned out good, for both of us… we both have done bad things… But… It'll be fine," she smiled at him, her smile watery from her tears, "and that's good. _We'll_ be fine."

Sans chuckled, squeezing his hand against hers—he got a squeeze back right away. His grin fell away, "just uh, don't mention anything about gaster. no one remembers him… and it'll just complicate things."

"I… think I've heard of him before. The River Person knows of him, you know," Frisk said, looking thoughtful for a moment before her features softened, "But… it's okay. I promise you, I won't."

The skeleton chuckled, deciding that _maybe_ their serious conversation should be over for now. They would have time to talk about other things, after all.

"c'mon kid, let's go to grillbz and get somethin' to eat."

At that, the human grinned.

.

 _Fin_

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 **Side notes:**

( **1** )—Thing towards another thing I wrote. Basically she's his mate, but yeaaahhhhh. He doesn't view her in a romantic light at this point, just in a protective fashion more than anything else. It's hard to explain.

 **My notes:** I'm not too happy with this, but whatever. I'll get better at writing with Undertale after a while, I think. Sans is annoying to write though 'cause puns aren't my thing. _Why can't he just be ironically sarcastic?_ Well… yeah. *wishes heavily* **Also, I write Frisk as a female because that's how I view the character. I know people say that the kid's agender, but I just... In most cases, people will view the character as their own gender, and since I'm a female I see them as female. I probably won't mention this again in the future, because I doubt my view on it will change (if it does, I'll state that explicitly).**


End file.
